The present invention relates in general to a method to be used for collecting defect images of a foreign substance and a defect generated in a thin film device manufacturing process on the basis of inspection information, and an apparatus for use in carrying out the method.
The production of thin-film devices, such as a semiconductor, a liquid crystal display device, a hard disk magnetic head, etc., involves a large number of processes. The number of process steps for performing such work reaches several hundreds of process steps on occasion.
When a foreign substance and anomalies in appearance, such as a break in wiring, etc., occur on a thin-film device due to imperfections and problems involving the manufacturing conditions of the processing equipment, the probability that a failure will occur in such a product becomes high, thus causing a degradation of the yield. Thus, in order to maintain a desired yield and to provide improvements in the manufacture, it is important to specify a defect in a produced device and take measures in connection therewith. Therefore, inspections, such as a foreign substance inspection, a visual inspection, etc., are executed for all main processes, and whether the processing or work is being done properly is monitored. Since the execution of all inspections effected on a substrate to be processed for all working processes is impossible from time and labor restrictions, inspections are normally conducted for substrates to be processed on a basis in lot units or processed substrate units, or in a combination thereof for every several series of process steps. Here, the substrate to be processed is a minimum unit in which product processing is carried out. It indicates one wafer, if a semiconductor is taken as an example.
When a wafer is examined for foreign substances by an inspecting device, for example, the surface of the wafer is scanned with a laser beam to detect the presence or absence of scattered light, so that information concerning the positions and the number of foreign substances which may be present n the wafer can be obtained. When a defect inspection is carried out that involves examination of a wafer for foreign substances and for a possible abnormality of each pattern together, information about the positions and number of significant points or the like can be obtained by, for example, capturing images of the wafer's circuit patterns by means of an optical magnifying imaging device and by making comparisons between the images and images obtained in other similar pattern regions adjacent thereto.
Here, the term “significant points” indicates points outputted as locations where abnormalities are found by the inspection performed by the inspecting device. The foreign substance and the anomalies that appear are subsequently represented as “defects”.
A decision as to the presence of an anomaly in a device is often made with a number of defects detected by the inspecting device as a density management index. When the number of defects exceeds a preset reference value, it is judged that a defect is present in the device. Then, each of the defects is imaged in an enlarged form by a reviewer, such as an optical microscope or a scanning electron microscope (hereinafter called “SEM”) or the like, on the basis of defect coordinate information detected by the inspecting device to obtain detailed information concerning the defect, such as the size, shape and texture thereof or the like. Detailed inspections, such as an elemental analysis, section observation, etc., are performed to specify a defective device and determine the content of it's the defective condition. Based on the result of this analysis thereof, countermeasures are taken for the device and the process is controlled to prevent degradation of the yield.
In order to bring such review work into a state of automation and high efficiency, a method for automatically acquiring enlarged images of a foreign substance and a defect in an efficient manner on the basis of inspection data outputted from a foreign substance inspecting device or a visual inspecting device has been described in Japanese Patent Laid-Open No. 2000-30652. Estimating the cause of the defects a from defect's visual information depends on high-level judgment of an analyzer, and differences among individuals and the time necessary for such a judgment present problems. Therefore, a method for automatically classifying defects in accordance with a specific rule has been described in Japanese Patent Laid-Open No. Hei 7(1995)-201946.
The significant points detected by the inspecting device are not necessarily limited to defects. There may be cases in which, for example, depressions and projections developed on a pattern, of such an extent that they cannot be recognized as defects, will be detected; components diffusely reflected from the edge portion of the pattern will be detected, a small variation in pattern shape, of such an extent that it cannot be judged as a defect, may be detected; or irregularities in luminance or color due to a small variation in the thickness, of such an extent that it cannot be judged as a defect, may be detected. Thus, when no defects are found in the significant points reviewed in detail, the circumstances may be interpreted to indicate that the device is free of defects, which serves as “disinformation” corresponding to a misdetection of the inspecting device. However, there may be a case in which a misdetection does not lead to such disinformation.
In the case of a defect inspecting device, for example, a circuit pattern is normally imaged using light having a wavelength in the range of ultraviolet light to visible light. Each of the areas for the same patterns located adjacent to each other and the shape of the circuit pattern are compared, and a section in which a difference results therebetween is detected as a defect. The image observed at the time of inspection is not limited to an image of the top surface of a device. When the surface of a substance is covered with a silicon oxide film, for example, the substance is optically transparent, and, hence, a foreign substance and a pattern that exist below the film are also imaged. Therefore, a defect that exists below the film is also detected. On the other hand, when the detailed reviewer consists of a SEM, an electron beam is applied onto a target, and secondary electrons and reflected electrons generated therefrom are brought into form of an image. In this case, the silicon oxide film remains nontransparent. Therefore, when no defect is observed during a detailed review using a SEM adapting to the defect detected by the defect inspecting device, a decision can not be made as to whether the results indicate disinformation or a below-film defect.
The concept of observing the structure of the inside of a specimen, a defect, a foreign substance, etc. through use of an electron beam having high energy has been described in Japanese Patent Laid-Open No. Hei 5(1993)-290786. However, a technique that makes it possible to obtain suitable observations that are compatible between a defect observation of the top surface and an internal observation has not yet been disclosed. Further, the concept of acquiring images under a plurality of observation conditions by use of an electron microscope and classifying defects according to the difference in visibility has been described in Japanese Patent Laid-Open No. 2001-93950. However, a method of bringing a review work operation into high efficiency according to the circumstances of a target defect has not been disclosed therein.